1. Field of the Invention
The present invention relates to handled thermoplastic bag structures which are especially designed to avoid stress concentration in those areas of the bag most susceptible to rupture such as a cut-edge which forms at the bag mouth or minute nicks and tears immediately adjacent to the bag mouth edge and caused as a result of separating forces developed in an individual bag along a perforate line, and during typical loading operations.
2. Description of the Prior Art
In the past, bags which were characterized by having carrying handles thereon were constructed using separate handle elements, distinct from the bag structure itself, which were fed for attachment adjacent to the open mouth portion of the bag. The manufacturing operation to produce such prior art structures with the separate process step of supplying handling element and applying them to the bag was quite cumbersome and uneconomical. More recently, however, bag structures have been developed, see for example U.S. Pat. Nos. 4,085,822; 3,352,411 and 3,180,557; the disclosures of which are incorporated herein by reference, wherein bags are formed so that the handle carrying elements are formed as an integral part of the bag structure itself, that is to say, the handles are actually an extension of the bag proper. An example of such a bag structure is one that is constructed from a flattened tube or a flattened side edge gusseted tube. A flattened portion of such a tube is cut off and sealed along its top and bottom edges. Conversely, such a bag may be formed by folding a piece of the thermoplastic material on itself, the bottom fold line constituting the bottom part of the bag and heat sealing the upper edge and side wall parts of the bag together. Next, a U shaped cutout is made in the upper portion of the bag to provide an opening or entrance for the introduction of goods to be packaged. The opposite edges of the upper portion of the bag structure immediately adjacent to the cutout area form loops which may be used to carry such bag structures when they are loaded. In the case of a gusseted tube such handle loops are reinforced, i.e., double ply thickness, by virtue of the presence of the re-entrant or gusset fold in the loop handle members.
Such aforedescribed prior art structure presents structural failure problems in those areas of the bag structure which are most susceptible to stress concentration when the handle loops of the bag are separated and temporarily suspended on a loading fixture for bag filling operations. One such filling operation and bag support structure are described in U.S. Pat. No. 4,062,170, the entire disclosure of which is incorporated herein by reference.
Such areas of stress concentration are usually located at areas adjacent to the lower portion of the bag handles. Additionally, it has been found when such bag structures are fabricated from high density polyethylene film there is a very pronounced tendency for tears to be initiated along the edge of cutout portions formed during cutting operations as the bag mouth is being produced. Such tears are usually in the machine direction of the film, i.e., in the direction in which the film is originally extruded and which usually corresponds, in the present instance, to the lengthwise direction of the bag, that is, from the bag top to the bag bottom. Such tears, once initiated, quickly propagate in the machine direction resulting in a bag failure.